1. Field of the Invention
This invention relates to semiconductor wafer processing, and more specifically to the elimination of amino groups and their subsequent effect on photoresist roughness.
2. Description of Related Art
Many substrates used in the field of manufacturing integrated circuit elements have high reflectivity that, upon exposure to ultraviolet light, causes light passing through a photoresist layer to be reflected upon the surface of the substrate and again incident into the photoresist layer. This has been shown to cause standing waves and patterned defects. Typically, antireflective coatings (ARC) have been placed between the resist and the substrate in order to prevent light reflection from the substrate into the resist. The ARC absorbs light directed towards the surface of the substrate, thus minimizing exposure of the resist from reflections. The ARC is commonly comprised of an organic polymer solution containing light-absorbing dye dispersed or dissolved therein to the surface of the substrate, or a polymer itself, which has radiation absorbing properties. Inorganic compounds such as silicon oxynitride, deposited by means of plasma enhanced chemical vapor deposition (PECVD), have been shown effective as antireflective coatings for shorter light wavelengths, such as the deep ultraviolet spectrum. However, even with an ARC layer, distortion of line profiles has been observed in the developed photoresist images. In part, reflections are not completely cancelled, and other factors contribute to unwanted photoresist exposure.
It is desirable to suppress reflections from underlying layers so that the photoresist is not exposed to the reflected light waves, which leads to variation in critical dimensions. The total distance that a light wave travels is determined by the thickness and index of refraction of the material that it passes through. If this thickness varies, as it will from one manufacturing process to another, the light waves reflected off a bottom surface will not be 180° out of phase with the light reflected off a top surface. Thus, destructive interference will not be complete, and light will reflect into the photoresist causing undesirable exposure.
Furthermore, contaminants that are incompatible with the photoreactive polymeric material can migrate into the photoresist layer from the ARC layer or other vicinal layer. These contaminants can poison the photoresist layer, and lead to the formation of a photoresist footing or T-top structure. These structures are anomalies in the otherwise precise dimensions of the exposed photoresist.
Line profile distortion has been shown to occur from the presence on the surface of the ARC due to amino (NH2) groups that settle during the PECVD process. Any delay depositing a photoresist layer after the ARC layer is deposited will expose the ARC layer to air and acidic airborne contaminants and/or basic contaminants at the substrate surface. These, in turn, will react with the amino groups to form outgrowths on the photoresist.
In U.S. Pat. No. 6,242,361 issued to Lee, et al., on Jun. 5, 2001, entitled “PLASMA TREATMENT TO IMPROVE DUV PHOTORESIST PROCESS,” an antireflective coating is deposited on a substrate through PECVD, and immediately thereafter, the substrate is placed in a gas discharge chamber where argon gas, oxygen gas, or a mixture of both is admitted with high density plasma. The oxide cap over the surface of the ARC immediately follows the ARC's deposition and is prior to exposure to air and later application of the photoresist. Importantly, Lee teaches that high density plasma having an ion density of about 109 to 1013 ions per cubic centimeter is necessary to carry out the invention. With this plasma enhanced treating of the ARC, T-tops and footing growth is significantly reduced along the edges of the lines formed in the photoresist.
In U.S. Pat. No. 6,417,559 issued to Moore, et al., on Jul. 9, 2002, entitled “SEMICONDUCTOR WAFER ASSEMBLIES COMPRISING PHOTORESIST OVER SILICON NITRIDE MATERIALS,” a silicon nitride layer having two distinct portions of different composition is taught, having a predominant nitride barrier over a silicon nitride layer. This layer promotes adhesion of the photoresist. Importantly, there is no antireflective coating formed between the silicon nitride layer and the photoresist. Instead, the photoresist is formed directly against the upper portion of the silicon nitride layer. Amino group transports due to impurities in the ARC are thus eliminated.
In U.S. Pat. No. 6,103,456 issued to Tobben, et al., on Aug. 15, 2000, entitled “PREVENTION OF PHOTORESIST POISONING FROM DIELECTRIC ANTIREFLECTIVE COATING IN SEMICONDUCTOR FABRICATION,” a dielectric spacer layer is taught to prevent reactive nitrogenous substance transport through the antireflective coating layer to the photoresist layer. An arrangement of silicon oxynitride as an ARC layer for a photoresist layer is disclosed as preventing out-diffusion of reactive nitrogenous substances so as to avoid poisoning the photoresist layer and consequent photoresist footing or pinching problems. In Tobben, the application of a specialized ARC layer with a dielectric spacer over the ARC layer prevents unwanted amino group transport.
The problems associated with prior art attempts to remove amino groups from the ARC deal substantially with process, such as, necessitating a plasma application, or applying a layer over the ARC and under the photoresist, where process time delays can lead to more aggressive amino group production. Furthermore, the applications of prior art processes to 193 nanometer technology is prohibitive.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a process that eliminates amino group transport to the photoresist layer while facilitating semiconductor wafer fabrication.
It is another object of the present invention to provide an alternative to plasma-enhanced applications for eliminating footings and T-tops in photoresist layers on semiconductors employing antireflective coatings.
It is a further object of the present invention to reduce line profile distortion in photoresist during processing.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.